Steep-edge absorption filter

ABSTRACT

There is disclosed glass compositions, i.e., filters characterized by steep edged absorption curves in the wave length range lambda 380 - 475 nm. The filters are prepared by heat treating glass samples having the following composition at a temperature between 550* and 620* C at which CdS + ZnS color centers are formed: SiO2 44-66 wt-%K2O8-24 wt-%ZnO12-24 wt-%B2O3 0-8 wt-%Na2O0-4 wt%Al2O3 0-3 wt-%MgO0-6 wt-%CaO0-12 wt-%BaO0-8 wt-%SrO0-12 wt%ZnS0.5-2.4 wt-%CdS0.5-1.5 wt-%

United States Patent [1 1 Ritze m1 3,754, 816 Aug. 28, 1973 STEEP-EDGE ABSORPTION FILTER Willi Rltu, Mainz, Mombach, Germany Assignee: Jenner Glnswerk Schott & Gem,

Mainz, Germany Filed: Nov. 15, 1967 Appl. No.: 683,228

Inventor:

[30] Foreign Application Priority Data Nov. 25, 1966 Germany J 32335 US. Cl. 350/311, 65/33, 65/111,

' 106/54 Int. Cl. G025 5/22, C030 3/22 Field of Search 350/311; 106/52,

References Cited UNITED STATES PATENTS 6/1932 Rising 65/33 UX OTHER PUBLICATIONS Weyl, W. A., Coloured Classes, The Society of Glass Technology, Sheffield. Mon., 1951.

Primary Examiner-Robert L. Lindsay, Jr. AuomeyBurgess, Dinklage and Sprung 5 ABSTRACT There is discloud glass compositions. i.e.. filters characterized by steep edged absorption curves in the wave length range A: 380 475 nm. The filters are prepared by heat treating glass samples having the following composition at a temperature between 550 and 620 C at which CdS ZnS color centers are formed:

1 Claim, 1 Drawing Figure Patented Aug. 28, 1973 3,754,816

-& 0.00 0.9a

070 0.00 v l V 050 I I 040 I 0.30 0.20

w-wy STEEP-EDGE ABSORPTION FILTER This invention relates to a filter having a steep edge absorption pattern in the wave length range of A 380 475 nm and having a net transmittance of 0.80.

Yellow glasses are known which have diminishing absorption bands at the short-wave length end of the visible spectrum, A 425 to 475 nm, net transmittance 0.80. These glasses are obtained through colloidal coloration by- CdS S of SiO -CaO-BaO-alkali oxide glasses following heat treatment. The aforesaid known colored glasses have the following disadvantages:

l. The absorption width of their steep edge curves AAat 9 l to 0.80 and 3 mm thickness is greater than 60 nm, and at 1 mm thickness it is greater than l00 nm.

2. ln filters having a thickness of l mm the absorption background is greatly brightened. It becomes necessary to use filters having a thickness equal to or greater than 3 mm in order to diminish the absorption background to 9 10' in the wave length range A of 400 430 nm.

3. The position or location of the absorption bands can be shifted only from A490 425 nm 6 0.80).

4. The manufacture of these colored glasses is subject to very exacting requirements and from batch to batch variations have to be expected as concerns the degree of steepness and location of the wave length.

The object of the present invention is to provide filters characterized by steep edged absorption curves in the wave length range A 380 475 nm which avoid the disadvantages as set out above.

Another object of the invention is to provide a method of manufacturing filters characterized by steep edged absorption curves in the wave length range A 380 475 nm which is capable of greater and consistent accuracy from one batch to the next.

As will be described in more detail hereinafter, these objects are achieved according to the invention by heat treating a glass of the following composition in the transformation range between 550 and 620 C to thereby form CdS ZnS color centers therein:

According to a preferred embodiment of the invention a basic glass having the following composition is heat treated at 580 1 3 C:

Weight Percen SiO, l .4 3,0, 3.9 K,O 22.2 ZnO 19.9 ZnS l .6 CdS l .0

It has furthermore been found advantageous for the total amount of the alkaline earth oxides plus zinc oxide present not to exceed 26 percent by weight.

The heat treatment of these glasses in this very narrow temperature range in the transformation region (i.e., between 570 and 620 C) results in the production of mixed color centers by the ZnS CdS, which determine the location (A 380 475 nm) and the steepness of the edge of the absorption curve. If the temperature is exceeded, the ZnS precipitates out too soon and the glass becomes cloudy. If the narrow ranges of 0.5 to 2.4 percent ZnS by weight and 0.5 to 1.5 percent CdS by weight are exceeded, only the CdS precipitates and this results in that the steepness of the edge of the absorption curve and of the location thereof, which then cannot be shifted to a shorter wave length, that is, it cannot be shifted below A 424 nm (6 0.80) towards the ultraviolet region. Further the curve edge of the filter is less steep and the filter has a cording to the invention have the following advantagesover the colored glasses of the prior art:

1. The absorption width of the steep edge A A of net transmittance G 10" to 0.80 amounts to less than 25 nm at a thickness of 1 mm (curves 1 and 2 of the drawing).

2. The absorption edge is steep down to 9 10' at a thickness of 1 mm (curves 1 and 2).

3. The location of the steep edge can be placed anywhere from A 475 nm to A 380 nm by heat treatment in the transformation region (6 0.80, 1 mm thickness) (Curve 2).

4. The absorption curve edge, even at a thickness of r 0.3 mm, is still steep down to 9 10 5. The absorption width of the steep edge A A of transmittance of G 10* to 0.80 is less than 60 nm at a thickness of 0. 15 mm.

6. The manufacture of these steep edge filter glasses is reproducible even on a large technical scale. The

location of the absorption curves steep edge at 9 s 0.80 can be accurately adjusted within 2 nm.

A typical filter having a composition having the advantages of the present invention together with the method of preparing the same is as follows:

EXAMPLE The following batch was mixed in the conventional glass mixing machine and was thereafter placed in ,a ceramic crucible furnace for about 16 hours at l,290 C.

COMPOSITION FORMULA FOR A BATCH OF Thereafter the batch was clarified at l,3l to l320 C for an additional l2 to 14 hours. It was then allowed to cool down to l,l80 C and stirred for about 3 to 4 hours down to 1,050" C. After an additional period of 5 which CdS ZnS color centers are formed.

I claim:

1. A filter having a steep edge absorption curve in the wavelength range A 380-475 nm which is a glass formed by heat treatment in the transformation range at 580 i 3 C for the formation ofCdS ZnS color centers, of a glass having the following composition:

SiO, 51.4 wt-% 8,0, 3.9 wt-% K 0 22.2 wt-% ZnO 19.9 wt-% ZnS l.6 wt-% CdS l.0 wt-% 

